This research project aims at establishing the following: 1) Induction of genital cancer in rat offspring by transplacental and transmammary exposure to diethylstilbestrol (DES); 2) Investigation of the effect of sex steroids (estrogens, progesterone, testosterone) on the course of rat pregnancy and exposed offspring; 3) Elucidation of the mechanisms by which DES and exogenous sex steroids influence development and differentiation of the urogenital apparatus in the rat; 4) Investigation of the relationship of sex steroid-induced disturbance in tranformation of vaginal Muellerian (columnar) epithelium into squamous epithelium and subsequent development of genital cancer, and 5) Determination of the usefulness of the pregnant rat as a screening model for substances potentially teratogenic and carcinogenic to human offspring.